Internal combustion engines may include central fuel injection (CFI) systems that inject fuel into an intake manifold. When fuel is injected into the engine intake, heat is transferred from the intake air and/or engine components to the fuel and this heat transfer leads to atomization of a portion of the fuel, which results in cooling of the engine components. Injecting fuel into the intake air (e.g., in the intake manifold, ports, etc.) lowers both the intake air temperature and a temperature of combustion at the engine cylinders. By cooling the intake air charge, a knock tendency may be decreased. This may also allow for a higher compression ratio, advanced ignition timing, and decreased exhaust temperature. Furthermore, lowered combustion temperature with fuel injection may reduce NOx, while a more efficient fuel mixture may reduce carbon monoxide and hydrocarbon emissions. In addition to CFI, fuel may be injected to intake runners via port injectors and/or directly into cylinders via direct injectors.
An example engine system with multiple fuel injectors is shown by Brehob et al. in U.S. Pat. No. 7,426,918. At the various locations of the injectors, there may be distinct fuel vaporization effects as well as fuel puddling effects. Accordingly, various approaches have been developed for adjusting the fueling schedule in engine systems having fuel injectors at different locations. In one example approach, as shown by Kirwan et al. in U.S. Pat. No. 6,176,222, the fueling schedule of each fuel injector is pre-emptively adjusted based on predicted fuel volatility, fuel vaporization effects, and expected fuel puddle dynamics. The prediction for manifold fuel injection is based on manifold conditions, such as manifold charge temperature, manifold air pressure, and engine speed.
However, the inventors herein have recognized potential issues with such systems. As one example, there may be a difference between the predicted amount of fuel atomization and puddle dynamics and the actual amount of fuel atomization and corresponding puddle dynamics following a fuel injection, due to transient engine conditions. In addition, fuel puddles formed at an intake manifold following manifold fuel injection may have an effect on port fuel puddles formed at an intake port. Further, an existing manifold fuel puddle may corrupt the predicted amount of vaporized fuel. As a result, the amount of fuel injected based on the prediction may not be sufficient for providing the desired level of cooling and for effective combustion. Inaccurate fueling may result in increased tendency for knock and the need for higher than intended spark retard usage, which in turn can cause an increase in fuel consumption. Further, based on the manifold conditions, such as based on how much fuel has vaporized into the manifold from an existing manifold fuel puddle, the charge cooling effect of the manifold fuel injection may vary. If the expected charge cooling is not provided, the manifold fuel injection may be rendered futile.
The inventors herein have identified an approach by which the issues described above may be at least partly addressed. One example method comprises: adjusting a ratio of fuel delivered to an engine via manifold injection relative to fuel delivered via one or more of port and direct injection based on a predicted charge cooling effect of the manifold injection, the charge cooling effect predicted based on each of a concentration of fuel vapor in the intake manifold, a temperature of a manifold surface onto which fuel is manifold injected, and air charge temperature. In this way, the fueling schedule may be adjusted based on predicted charge cooling including feedback from a manifold charge temperature (MCT) sensor, allowing fuel puddle dynamics to be more reliably accounted for.
As one example, based on engine operating conditions, an engine controller may determine an initial fuel injection profile including an amount of fuel to be delivered via manifold fuel injection (e.g., via a central manifold fuel injector or CFI), and a remaining amount of fuel to be delivered via one or more of port and direct fuel injection. As the fuel injected via the CFI atomizes in the intake manifold, the intake manifold may be cooled, creating a charge cooling effect. The controller may predict the charge cooling effect of the upcoming fuel injection event based on the temperature of a manifold surface onto which the fuel is injected via the CFI, and further based on a concentration of fuel vapor on the intake manifold (including fuel that has vaporized from a manifold fuel puddle). In one example, the charge cooling effect may be predicted based on a measured charge cooling effect of an immediately previous manifold fuel injection. For example, based on a change in manifold temperature from before and after the immediately previous manifold fuel injection, as measured by a manifold charge temperature sensor, the controller may estimate the amount of fuel that vaporized versus the amount of fuel that condensed in the manifold, and further estimate the change in manifold surface temperature. The controller may also update fuel puddle dynamics for a manifold fuel puddle accordingly. If the predicted charge cooling effect is more than a threshold amount, then the controller may fuel the engine in accordance with the determined fuel injection profile. Optionally, the manifold fuel injection amount may be updated with a correction factor based on the charge cooling learned on the previous manifold injection and a puddle correction factor based on the change in puddle size learned on the previous manifold injection. However, if the predicted charge cooling effect is less than the threshold amount, then in anticipation of insufficient charge cooling at the manifold, the fuel injection profile may be updated to decrease the manifold fuel injection amount. In one example, a direct fuel injection amount may be correspondingly increased so as provide a charge cooling effect in the cylinder.
In this way, by adjusting a manifold fuel injection based on a predicted charge cooling effect of the injection, the advantages of a manifold fuel injection may be better leveraged. By measuring a change in manifold temperature following a manifold fuel injection, an amount of fuel atomized versus an amount of fuel remaining in the liquid phase, following a manifold injection, may be accurately estimated. This enables size and dynamics of a manifold fuel puddle generated after each injection to be accurately determined. The technical effect of accurately estimating the amount of fuel atomized, the amount of fuel condensed, and the corresponding puddle dynamics is that subsequent fueling schedule may be effectively adjusted to provide a desired level of manifold cooling. By providing manifold cooling, engine performance and fuel efficiency may be improved.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.